Analysis and design of triple-rotor axial-flux spoke-array vernier permanent magnet machines

Abstract

This paper presents a triple-rotor axial-flux spoke-array vernier permanent magnet (TR-AFSAVPM) machine to enhance the performance of vernier machines. By cooperating spoke-array rotor and coil-wounded winding, power factor and torque density of the proposed machines are much improved and their copper utilization is reduced as well comparing with conventional vernier machines. Firstly, the machine structure and operation principles are introduced. After that, analytical equations of the machine back-EMF and torque are derived to reveal its features. Based on both quasi-3D finite element analysis (FEA) and 3D-FEA, its high torque density performance is verified and a set of optimized machine sizing specifications is ultimately settled. A fractional slot axial-flux permanent magnet machine and an axial-flux surface vernier permanent magnet machine are designed to compare with the proposed machine. Analysis results show that the TR-AFSAVPM machine has high power factor, viz. 0.97 and high torque density, viz. 24.2kNm/m3. A prototype has been designed and is being manufactured to validate the results.